DESCRIPTION

SSL_CTX_set0_chain() and SSL_CTX_set1_chain() set the certificate chain
associated with the current certificate of ctx to sk.

SSL_CTX_add0_chain_cert() and SSL_CTX_add1_chain_cert() append the single
certificate x509 to the chain associated with the current certificate of
ctx.

SSL_CTX_get0_chain_certs() retrieves the chain associated with the current
certificate of ctx.

SSL_CTX_clear_chain_certs() clears any existing chain associated with the
current certificate of ctx. (This is implemented by calling
SSL_CTX_set0_chain() with sk set to NULL).

SSL_CTX_build_cert_chain() builds the certificate chain for ctx normally
this uses the chain store or the verify store if the chain store is not set.
If the function is successful the built chain will replace any existing chain.
The flags parameter can be set to SSL_BUILD_CHAIN_FLAG_UNTRUSTED to use
existing chain certificates as untrusted CAs, SSL_BUILD_CHAIN_FLAG_NO_ROOT
to omit the root CA from the built chain, SSL_BUILD_CHAIN_FLAG_CHECK to
use all existing chain certificates only to build the chain (effectively
sanity checking and rearranging them if necessary), the flag
SSL_BUILD_CHAIN_FLAG_IGNORE_ERROR ignores any errors during verification:
if flag SSL_BUILD_CHAIN_FLAG_CLEAR_ERROR is also set verification errors
are cleared from the error queue.

Each of these functions operates on the current end entity
(i.e. server or client) certificate. This is the last certificate loaded or
selected on the corresponding ctx structure.

SSL_CTX_select_current_cert() selects x509 as the current end entity
certificate, but only if x509 has already been loaded into ctx using a
function such as SSL_CTX_use_certificate().

SSL_CTX_set_current_cert() changes the current certificate to a value based
on the op argument. Currently op can be SSL_CERT_SET_FIRST to use
the first valid certificate or SSL_CERT_SET_NEXT to set the next valid
certificate after the current certificate. These two operations can be
used to iterate over all certificates in an SSL_CTX structure.

SSL_set_current_cert() also supports the option SSL_CERT_SET_SERVER.
If ssl is a server and has sent a certificate to a connected client
this option sets that certificate to the current certificate and returns 1.
If the negotiated ciphersuite is anonymous (and thus no certificate will
be sent) 2 is returned and the current certificate is unchanged. If ssl
is not a server or a certificate has not been sent 0 is returned and
the current certificate is unchanged.

All these functions are implemented as macros. Those containing a 1
increment the reference count of the supplied certificate or chain so it must
be freed at some point after the operation. Those containing a 0 do
not increment reference counts and the supplied certificate or chain
MUST NOT be freed after the operation.

NOTES

The chains associate with an SSL_CTX structure are copied to any SSL
structures when SSL_new() is called. SSL structures will not be affected
by any chains subsequently changed in the parent SSL_CTX.

One chain can be set for each key type supported by a server. So, for example,
an RSA and a DSA certificate can (and often will) have different chains.

The functions SSL_CTX_build_cert_chain() and SSL_build_cert_chain() can
be used to check application configuration and to ensure any necessary
subordinate CAs are sent in the correct order. Misconfigured applications
sending incorrect certificate chains often cause problems with peers.

For example an application can add any set of certificates using
SSL_CTX_use_certificate_chain_file() then call SSL_CTX_build_cert_chain()
with the option SSL_BUILD_CHAIN_FLAG_CHECK to check and reorder them.

Applications can issue non fatal warnings when checking chains by setting
the flag SSL_BUILD_CHAIN_FLAG_IGNORE_ERRORS and checking the return
value.

Calling SSL_CTX_build_cert_chain() or SSL_build_cert_chain() is more
efficient than the automatic chain building as it is only performed once.
Automatic chain building is performed on each new session.

If any certificates are added using these functions no certificates added
using SSL_CTX_add_extra_chain_cert() will be used.

RETURN VALUES

SSL_set_current_cert() with SSL_CERT_SET_SERVER return 1 for success, 2 if
no server certificate is used because the ciphersuites is anonymous and 0
for failure.

SSL_CTX_build_cert_chain() and SSL_build_cert_chain() return 1 for success
and 0 for failure. If the flag SSL_BUILD_CHAIN_FLAG_IGNORE_ERROR and
a verification error occurs then 2 is returned.